Duplex balancing arrangement



March 16 1926. 1,576,566

H. A. AF F EL DUPLEX BALANCING ARRANGEMENT Filed April 1. 1920 IN V EN TOR.

W ATTORNEY Patented Mar. 16, 1926.

UNITED STATES- 1,576,566 PATENT OFFICE.

HERMAN A. AFFEL, F BROOKLYN, NEW YORK, ASSIGN OR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

DUPLEX BALANCING ARRANGEMENT.

Application filed April 1,

To all whom it may concern.

Be it known that I, HERMAN A. AFFEL, a citizen of the United States, residing at Brooklyn, in the county of Kings and State 5 of New York, have invented certain Improvements in Duplex Balancing Arrangements, of which the following is a specification.

This invention relates to means for the simultaneous transmission of currents of a plurality of channels, and more particularly to a novel combination of selecting networks and balancing networks for preventing interference between the transmitted channels 1 without causing excessive loss of energy in the said interference preventing networks.

In multiplex communication or transmission systems designed for the simultaneous transmission of currents constituting a plurality of bands or channels, each band or channel representing either a single frequency or group of frequencies based upon some fundamental frequency, interference between the fundamental frequencies of the respective channels may be prevented by means of selective networks, but interference may incidentally result if there happen to be present any harmonics of one of the fundamental frequencies which fall within the range of frequencies of the other channel. Investigations of interference between power transmission lines and signalin circuits have revealed in the signaling c1rcuit frequencies as high as the 30th harmonic of the fundamental frequency of the power line so it may readilybe seen that it is often difficult to prevent interference in multiplex systems by selective networks alone, particularly where the interference is produced by a powerful transmitting source whose harmonics feed into a local receiving circuit of another channel.

Likewise, systems which are designed to prevent interference between channels by means of balancing networks whose function is to balance the line for one of the fundamental frequencies are objectionable because of the excessive energy absorption which takes place in the balancing network.

It is the object of the present invention to prevent interference between transmission channels by combinin in a novel way selective networks and ba ancing networks, the selective networks functioning to prevent interference between the fundamental fre- 1920. Serial N0. 370,439.

quencies of the channels, and the balancing line, and therefore no loss of energy of that fundamental frequency would occur.

This invention will be more clearly understood from the following description read in connection with the attached drawing, of which Figure 1 shows the application of the invention to as stem for the transmission of current of tel ephonic frequencies over a power transmission line, and Figure 2 shows the application of the invention to a duplex radio system.

In Fig. 1, L represents a power transmission line which is adapted for the simultaneous transmission of power and signaling currents. G, represents an alternating current generator which is connected with the transmission line L,, the fundamental frequency of which may be assumed for purposes of illustration, to be between 0 and cycles. Connected into the transmission line on each side of the point of connection of the generator thereto are the low-pass filters LPF, and LPF respectively, which may be of the well-known t pe disclosed in the patent to Campbell, N b. 1,227,113, dated May 22nd, 1917 Also connected with the transmission line is a balancing network N, which is designed to balance the transmission line L, with respect to such harmonics of the fundamental power frequency which would be most liable to interfere with the frequencies embraced within the signaling channel transmitted over the said line. Also connected with the line L, by means of the triple winding transformer 1 is a telephone .circuit represented schematically by the receiver R,, transmitter T and connecting circuits. Between the transformer 1 and the line L, are inserted high-pass filters HPF and HiPF which preferably are of the Campbell type heretofore referred to and are designed to transmit therethrough, with minimum attenuation, currents of signaling or telephone frequencies.

Fig. 2, illustrates the application of partial harmonic balancing to a duplex radio system which is intended for the simultaneous transmission and reception of a plurality of different frequencies. In the drawing A, represents an antenna having connected therewith the receiving circuit 1 and the transmitting circuit 2, the latter being represented as a Poulsen type are circuit which is a type of circuit in which the production of harmonics is notoriously large. The receiving circuit is coupled to the antenna circuit by means of the transformer 3 and the transmitter circuit is directly connected with the midpoint of the antenna winding of the transformer.

Connected with the transformer is a balancing network N which is resonant and whose impedance is adjusted to simulate the corresponding impedance of the antenna to certain predetermined harmomcs of the transmitted frequency F which are most liable to interfere with the received frequency F The network N on the other hand, is designed to have high impedance at the fundamental frequency F The circuit 1 which is tuned to reception frequency 1s connected across the input side of the detector D which in turn is connected with the receiver R,. Connected with the transmitting circuit 2 may be any well-known form of transmitting device T Having in mind the foregoing descriptlon of the parts of theJapparatus set forth in Figures 1 and 2, and the function performed by each part, the invention will be clear from the following description of the mode of operation of each of these circuits.

In the arrangement shown in Fig. 1, the generator Gr may apply current to the transmission line of a pre etermined frequency varying from 0 to 60 cycles and the slgnaling circuit may simultaneously apply current extending from 200 cycles upward. Interference between the fundamental frequency of the power channel and the band of frequencies of the signaling channel 15 prevented by means of the arrangement of the low-pass filters and of the high-pass filters. Since it is well-known that hi h harmonics as far as the thirtieth may present in power transmission circuits, it is desirable in order to prevent these harmonics from interfering with the signaling channel, to balance by meansof a suitable network the transmission line for these frequencies. In the arrangement shown, the lowass filters LPF and LPF are so arrange in the circuit as to impress the power voltage across both the transmission line and the selective network N Since the network is so designed as to offer relatively high impedance compared with the transmission line itself to the fundamental power frequency and to simulate the transmission line impedance for the higher harmonics, it will be seen that 'substantially'no current of the fundamental power freiguency will be lost in the balancing network ,-but, on the other hand, currents of the higher frequencies which may in a slight degree pass through the low-pass filters due to the large amountof energy in the power circuit will be balanced by the network N and therefore will not interfere with the signaling channel.

Although the principle of this invention has been disclosed in an arran ement for transmitting signaling current of telephonic frequency over a circuit simultaneously with the transmission of power current, it is not limited to such specific structure or to such frequencies but may be applied to other arrangements involving different frequencies. Thus, for example, by means of the balancing transformer 1, which is shown connected through the high-pass filters HPF and HPF, on the line and network sides respec tively, the line L may be connected to a four-wire telephone, carrier telephone, carrier telegraph or other signaling circuit. Furthermore, if desirable, four-wire operation may be discarded and a two-wire connection substituted by bridging across a.

throu h connection between the two highpass lters.

The arrangement disclosed in Fig. 2 represents the application of this invention to prevent interference in du lex radio systems between the undesirab e harmonics of the transmitted frequency and the received frequency. In such systems it is found that when oscillations are being transmitted at a frequency F from the antenna A simultaneously with the reception from a distant station of a frequency F the harmonics or multiples of F may be sufliciently close to the reception frequency F as to cause troublesome interference in receiving even though the fundamental frequencies are sufficiently separated as not to interfere. It is the object of the present invention to minimize or prevent such interference.

If, in transmitting oscillations of the frequency F there are set up in the antenna circuit any harmonics of frequency F current of the frequency of these harmonics will flow in the antenna winding of transformer 3 in both directions from its midpoint, and to substantially the same degree ecause the network N is adjusted to simulate the impedance of the antenna to these harmonics of frequency F Since the current resulting from the objectionable harmonies of F flows in opposite directions from the midpoint of the antenna winding of transformer 3, substantially no reaction will be set up in the receiving circuit 1, tuned to reception frequency. Furthermore, since the network N has high impedance at the fundamental transmitting frequency F substantially no current at this frequency will flow through the network N consequently there will be no energy lost of the fundamental transmitting frequency. Also, since the receiving circuit 1 is tuned to a frequency that is fundamentally different from the transmitting frequency F there will be no undesirable reaction betweenbasic frequencies F and F of the transmitting and the receiving channels, respectively.

From the foregoingdescri tion of this invention it will be seen that t ere has been disclosed the novel combination of two wellknown means of preventing interferences between transmission channels of a plurality of frequencies, applicable either to wire or wireless transmission systems, which reduces to a minimum the loss incidental to the use of such interference preventing devices.

Although this invention has been disclosed in certain specific forms, it is to'be understood that it is not thus limited but is capable of embodiment in other and widely different forms without departing from the spirit and scope of the appended claims.

What is blaimed is: v

1. In a signaling system adapted for the simultaneous transmission of frequencies constituting a plurality of channels of transmission the combination of a transmission line, means for impressing a plurality of groups of frequencies on the said line, selective networks adapted to discriminate between thefundamental frequencies of the said groups, and a balancing network designed to balance said line for predeterminate harmonics only of one of said groups which are liable to interfere with the frequencies of the other of said groups.

2. In a signaling system adapted for the simultaneous transmission of frequencies constituting a plurality of channels of transmission the combination of a transmitting circuit, means for applying a plurality of groups of frequencies to the said circuit, selective networks adapted to transmit frequencies of the desired group and to attenuate frequencies of the undesired group, and a balancing network simulating the impedance of the said line for harmonics of the frequencies of the'first group and having higher impedance for the fundamental frequencies of the said first group.

3. In a signaling system adapted for the simultaneous transmission of power and signaling currents, the combination of a transmission circuit, means for impressing current of power frequency upon the said circuit, means for impressin current of signaling frequency upon sai circuit, selecting networks adapted to prevent interference between currents of power frequency and signaling frequency, and a balancing network adapted to simulate the line impe ances for suchharmonics of the power frequency as are liable to interfere with the said signaling frequency.

4. In a signaling system adapted for the simultaneous transmission of power and signaling currents, the combination of a common transmission circuit, means for impressing current of power frequency upon said circuit, a balancing network connected with said circuit simulating the impedances of the transmission circuit for certain predetermined harmonics of the said funda-' mental power frequency, low-pass filters connected with the said transmission circuit on the line side and the network side of the point of application of the power current thereto, means for applying current of signaling frequency to the said line circuit comprising signaling apparatus, a triplewinding transformer and highass filters inserted between the said trans ormer and the said line, and balancing network respectively.

harmonics of the power circuit whereby the said line circuit is balanced and the said harmonics are prevented from interfering with the signaling currents.

6. In a signaling system adapted for the simultaneous transmission of frequencies constituting a plurality of channels of transmission, the method of transmitting the carrier signaling currents over a power transmission line which consists in balancing the said line for those harmonics of the power frequency capable of interfering with the signaling frequency, applying the said power frequency to the said line and suppressing by filtering the harmonics of the said power frequency, and selecting by filtering the said carrier currents, thereby preventing interference between channels.

7. In an electrical transmission system adapted for the simultaneous transmission of frequencies constituting a plurality of distinct channels of transmission, the combination with a transmission circuit of a second circuit having a source of current of definite frequency connected therewith, a balancing network connected with the said transmission circuit whose impedance simulates the transmission circuit for certain harmonics of the frequency impressed on said circuit by said second circuit, and having higher impedance for the fundamental frequency of the said second circuit, and a third circuit having means for the transmission and reception of currents whose freonly of the fundamental frequency of the 10 quencies differ from that produced by the power currents, and preventing interference said first circuit. etween said fundamental power frequency 8. In a system for the simultaneous transand the signaling frequency byfiltering the mission of signaling currents and power respective frequencies; currents over the same transmission line, In testimony whereof, I have signed my 16 the method of eliminating interference bename to this specification this 30th day of tween the said currents which consists in March 1920. balancing the said line for the harmonics HERMAN A. AFFEL. 

